major and minor sources and for differing locations, and that it might not be possible to
identify and model all PSD sources. Some of these issues are described in Appendix B.
These uncertainties diminished the possible relevance of the MESOPUFF II results but do not
impair the objectives of the demonstration application.
Further discussions with IWAQM members led to the idea of reducing the scope of the PSD
source application of MESOPUFF II and adding an additional analysis using hypothetical
sources. A proposal was developed, whereby the original scope would be changed to:
• Prepare 5 years (1988-92) of meteorological data using MESOPAC, suitable for future
applications in the region. This task would remain the same.
• Simulate 3 years (36 contiguous months selected from 5 year period 1988-92) using
MESOPUFF II with selected PSD sources, using actual source data collected from EPA
Region III states.
• Perform 24 additional MESOPUFF II simulations using hypothetical sources at varying
distances from Shenandoah NP to provide some insight into the relationship between
distance from Shenandoah NP and potential PSD and AQRV impacts.
This modified modeling approach still accomplished the original objectives of preparing 5
years of meteorological data for future applications, going through and documenting the
modeling process for actual PSD sources, and using the modeling results to evaluate the longterm
PSD and AQRV impacts (over a 3-year period, instead of 5 years). By modifying the
scope in this way, the total number of MESOPUFF II simulations remained constant, and the
additional effort to prepare the source ring data was not significant. Hence, we were able to
obtain two useful modeling results instead of just one, and did not relinquish the original
objectives of the demonstration modeling exercise.
The remainder of this section describes model input preparation and application for the PSD
source analysis. This section is structured to provide discussions of issues, proposed approach
(protocol), problems, and resolutions for each step of the modeling process. The impact
versus distance analysis is described in Section 4.
MODELING DOMAIN DEFINITION
MESOPUFF II is suitable for simulating the mesoscale transport and dispersion of air
pollutants from a source or group of sources, and estimating their impacts on remote receptors
at distances of ten to hundreds of km downwind (Scire et al., 1984). The MESOPUFF II
modeling system utilizes three modeling grids. The meteorological grid is the largest; the
computational grid may be smaller than the meteorological grid or the same size, but must be
of the same resolution. The sampling grid may be smaller than the computational grid and
may be of higher resolution. The errors resulting from the projection of a curved surface onto
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